1. Field of the Invention
The present invention relates to a PIN type semiconductor photoelectric conversion device using a non-single-crystal semiconductor.
2. Description of the Prior Art
Heretofore there has been proposed a PIN type semiconductor photoelectric conversion device using a non-single-crystal semiconductor.
The PIN type semiconductor photoelectric conversion device comprises a laminated member having a first non-single-crystal semiconductor layer of a first conductivity type (P or N conductivity type), an I-type second non-single-crystal semiconductor layer and a third non-single-crystal semiconductor layer of a second conductivity type reverse from the first conductivity type (that is, N-type when the first non-single-crystal semiconductor layer is P-type, or P-type when the latter is N-type), and first and second electrodes making ohmic contact with the first and third non-single-crystal semiconductor layers, respectively.
When irradiated by light on the side of the first non-single-crystal semiconductor layer of the laminated member, such a PIN type semiconductor photoelectric conversion device performs a photoelectric conversion through the following mechanism. That is to say, the incident light passes through the first non-single-crystal semiconductor layer to reach the second non-single-crystal semiconductor layer, wherein it is absorbed. In consequence, carriers (electron-holes pairs) are created in the second non-single-crystal semiconductor layer. The carriers migrate into the first and third non-single-crystal semiconductor layers and then reach the first and second electrodes. Accordingly, a current corresponding to the intensity of the incident light is supplied to a load connected across the first and second electrodes.
In such a PIN type semiconductor photoelectric conversion device, as described above, incident light passes through the first non-single-crystal semiconductor layer to reach the second non-single-crystal semiconductor layer, wherein it is absorbed to create carriers therein.
However, all the light incident on the second non-single-crystal semiconductor layer through the first non-single-crystal semiconductor layer is not always absorbed by the second non-single-crystal semiconductor layer but a portion of the incident light passes through the third non-single-crystal semiconductor layer towards the second electrode.
IN the PIN type semiconductor photoelectric conversion device of the conventional structure described above, the second electrode does not reflect light but, if it does, it has only a small reflection coefficient. On account of this, in the prior art PIN type semiconductor photoelectric conversion device, that portion of the incident light which passes through the third non-single-crystal semiconductor layer towards the second electrode is scarcely utilized for photoelectric conversion and is dissipated in the second electrode.
Therefore, the conventional PIN type semiconductor photoelectric conversion device possesses the defects of low utilization efficiency of incident light and hence low photoelectric conversion efficiency.
Furthermore, in the PIN type semiconductor photoelectric conversion device of the above-described structure, the carriers created in the second non-single-crystal semiconductor layer migrate into the first and third non-single-crystal semiconductor layers and thence to the first and second electrodes. It is therefore desired that the first and second electrodes make excellent ohmic contact with the first and third non-single-crystal semiconductor layers, respectively.
It is general practice, in the conventional PIN type semiconductor photoelectric convension device that when the first non-single-crystal semiconductor layer of the laminated member is a non-single-crystal semiconductor on the side of incidence of light, the first electrode is formed by a light transparent conductive layer and the second electrode is formed of metal.
However, the first and second electrodes in the conventional PIN type semiconductor photoelectric convension device are formed without regard to the impurities contained in the first and third non-single-crystal semiconductor layers for imparting thereto respective conductivity types.
On account of this, the ohmic contact between the first electrode and the first non-single-crystal semiconductor layer and between the second electrode and the third non-single-crystal semiconductor layer is not very good in the conventional PIN type semiconductor photoelectric convension device.
Accordingly, the prior art PIN type semiconductor photoelectric conversion device has the defect of low photoelectric conversion efficiency in this regard also.